FYN TYROSINE KINASE ASSOCIATED WITH FC-EPSILON-RII/CD23 - POSSIBLE MULTIPLE ROLES IN LYMPHOCYTE-ACTIVATION

Expression of low-affinity Fc receptor for IgE (Fc-epsilon-RII), which is identical to the lymphocyte differentiation antigen CD23, is associated with activation of lymphoid cells. The mechanism of signal transduction through Fc-epsilon-RII/CD23 was dissected by transfection of cDNA coding for Fc-epsilon-RII to the YT human natural killer-like cell line, activation of which was easily detected by the induction of interleukin 2 receptor/p55(Tac). Cross-linking of Fc-epsilon-RII/CD23 with H107 anti-Fc-epsilon-RII monoclonal antibody markedly enhanced interleukin 2 receptor/p55 expression on the YT cells transfected with Fc-epsilon-RII cDNA (YTSER cells). Similar induction of interleukin 2 receptor/p55 by the cross-linking of Fc-epsilon-RII was observed on an Epstein-Barr virus-transformed B-cell line, 3B6, and fresh leukemic cells isolated from a patient with B-cell chronic lymphoblastic leukemia. Thus Fc-epsilon-RII/CD23 provides activation signals not only in YTSER cells but also in activated B cells. A possible involvement of protein-tyrosine kinase in the Fc-epsilon-RII-mediated signal transduction was studied. Fc-epsilon-RII was physically associated with a src family tyrosine kinase p59fyn and not with p56lck, which was also found in YT cells. Recently it was reported that p59fyn was associated with T-cell antigen receptor. Our results collectively suggest the multiple functions of p59fyn that may be implicated in Fc-epsilon-RII-mediated activation signal in YT cells.